The present invention relates to a disk array system, and more particularly to a control method for backing up its data to an external device.
For backing up the data of a disk array system, a differential backup method can be used to prevent the size of backup data from being enormously increased.
Using a file basis differential backup method for a disk array system having a network file server function and a storage area network function increases the load on a local area network that is used for data exchange during regular operation by host computers. Because the storage area network function cannot specify files and the network file server function has to be used for the method. In some cases, it is necessary to make a backup while regular operations implemented by the network file server function are halted.
Meanwhile, the disk array system having the network file server function and storage area network function uses a technology called “NAS over SAN”. When this technology is used, the data passing through a local area network is limited to file names, file attributes, and other items of file information, and the data contained in files are exchanged via a storage area network. When a backup is made with this technology, the backup data and the data exchanged for regular operations both pass through a storage area network.
In a system described in JP-A No. 112669/2000, a disk unit is provided with an area for temporarily storing backup data for the purpose of adjusting the speeds of the disk unit and external backup storage. This area does not store part of backup data and cannot possibly reduce the size of backup data.
In a system described in JP-A No. 347811/2000, a volume of a disk unit is made redundant for data storage purposes. This system can back up data within the disk unit. However, if the data is to be transferred out to an external device, the size of backup data does not decrease.